Conventional processes for the manufacture of components in treated steel from untreated steel in the form of bars, strips or coils, for example of springs, stabilizing bars or rail spring clips for railways, consist of a large number of operations.
As an example, the various successive operations of a conventional process for the manufacture of springs will be given below:
unwinding of the coils, flattening, descaling and grinding, PA1 austenizing heating in an oven with a protective atmosphere, PA1 hot forming, PA1 oil quenching, PA1 tempering in an oven, PA1 cooling, PA1 clamping, PA1 cooling to room temperature, PA1 prestress shot-blasting, PA1 tempering after shot-blasting, PA1 protecting (painting or plastifying), PA1 curing or crosslinking, PA1 cooling to room temperature, PA1 testing. PA1 forming or preforming the components cold, PA1 austenizing heating of the components, preferably in a fluidized bed bath or using induction, PA1 quenching the components in a fluidized bed bath, PA1 tempering the components, preferably in a fluidized bed bath, PA1 shot-blasting, PA1 optionally final cold forming of the components, PA1 protecting. PA1 heating the steel to a temperature above the transition point (austenizing), PA1 isothermal quenching in a fluidized bed bath, immediately following the austenizing heating, PA1 forming the components under mild conditions.
This conventional process comprises in particular a large number of stages of change in temperature, each of which involves considerable energy expenditure and costly plant. Furthermore, hot forming and oil quenching are operations which take place in difficult working and safety conditions. Lastly, oil quenching is an operation which gives rise to pollution due to the release of harmful smoke and vapours and due to the washing to which the components must be subjected after the oil quenching.
The process according to French Patent Application No. 2,391,789 already partly remedies the disadvantages listed above. This process, intended especially for the manufacture of rail fastenings, comprises the following stages:
However, this known process still has a certain number of disadvantages. In particular, it involves two operations of raising the temperature (austenizing heating before quenching, tempering after quenching). Furthermore, since the components are subjected to a forming or at least a preforming, cold, before any heating, it is impossible to carry out this heating on continuous material, for example in strip form.